The present invention relates to air-moving fans, and is more particularly directed to a heat exchanger assembly in which a fan draws or forces air through a heat exchanger coil. The invention specifically concerns the employment of a stator row with a propeller fan which moves air through a heat exchanger coil.
In a specific embodiment described hereafter, a stator row is applied beneficially to a packaged terminal air conditioner (PTAC), and would also be appropriate for room air conditioners or other similar devices.
A packaged terminal air conditioner is a unit having an interior or indoor side connected to an exterior or outdoor side through a penetration in a wall of a building. These units are generally used both in summer as an air conditioner for cooling and in winter as a heat pump for heating. The PTAC generally uses the same motor and drive shaft to power a centrifugal fan on the interior side and a propeller fan on the exterior side.
It has long been a goal in the industry to increase the air moving efficiency of the fans. This yields a dual benefit of requiring less electrical power and also reducing the noise level due to the fans.
Although stators in general are well known, e.g., in various compressors, they have not been used widely in the heating, ventilation, and air conditioning (HVAC) field, and have never been applied in PTAC units.
One combination of propeller fan with a stator assembly has been previously described in Gray, U.S. Pat. No. 4,548,548 for use in an automotive environment. In that patent, the fan is intended to blow air through a heat exchanger, and a circular stator placed immediately after the fan to direct the exhaust axially. The intention there is to remove rotational components, and provide smoother air flow through the heat exchanger. The stator assembly of the Gray patent forms part of the spider or frame that suspends the fan and motor in front of the heat exchanger. The stator there was also specifically intended for use with a so-called banded fan where the fan blade tips are connected by a circumferential skirt. In the Gray patent, the stator is circular in cross-section because it is integral to the fan-motor system and because it is designed to accommodate the flow field dominated by the fan. This is good practice when either the effective face area of the fan is approximately equal to the face area of the coil, or the axis of the fan coincides with the geometric center of the coil face.
However, when the face area of the coil is significantly larger than the face area of the fan, and/or the axis of the fan is offset from the geometric center of the coil, the stator placement and geometry must account for diffusion in order to achieve maximum benefit. This is critical because it is quite difficult to diffuse or expand the airstream from the circular geometry and discharge area of the fan to the larger and/or offset rectangular geometry of the coil. Maximum diffusion is necessary to minimize the natural tendency towards non-uniform air flow across the face of the coil with the concomitant increase (relative to uniform flow) in air-side coil pressure loss and under-utilization of heat transfer surface.
To maximize diffusion in order to achieve favorable control of the above-mentioned effects, it is beneficial to place the stator against the coil and to configure its overall geometry to match the coil face area. This allows the centrifugal force due to swirl to facilitate the outward diffusion process and, consequently, maximize uniform flow across the face of the coil. If the stator were placed generally at the fan discharge (Gray patent), the swirl velocity component would be removed prior to the diffusion process and, hence, would be unavailable to achieve the requisite diffusion.